A large number of organic electroluminescence (EL) devices each using an organic substance have been developed because of their potential to find applications in solid light emission type, inexpensive, large-area, full-color display devices. In general, an organic EL device is constituted of a light emitting layer and a pair of opposing electrodes between which the layer is interposed. Light emission is the phenomenon in which when an electric field is applied between both the electrodes, an electron is injected from a cathode side and a hole is injected from an anode side, and further, the electron recombines with the hole in the light emitting layer to produce an excited state, and energy generated upon return of the excited state to a ground state is emitted as light.
A conventional organic EL device was driven at a voltage higher than the voltage at which an inorganic light emitting diode is driven, and had emission luminance and luminous efficiency lower than those of the diode. In addition, the properties of the device deteriorated remarkably, so the device has not been put into practical use. A recent organic EL device has been gradually improved, but actually, additionally high luminous efficiency and an additionally long lifetime of the device are still requested.
For example, a technology involving the use of a single monoanthracene compound as an organic light emitting material has been disclosed (Patent Document 1). However, the technology is not practical because of, for example, the following reasons. That is, a luminance of only 1650 cd/m2 is obtained at a current density of 165 mA/cm2, and efficiency is 1 cd/A, which is an extremely low value. In addition, a technology involving the use of a single bisanthracene compound as an organic light emitting material has been disclosed (Patent Document 2). However, an improvement for putting the technology into practical use has been requested because efficiency is as low as about 1 to 3 cd/A. Meanwhile, a long-lifetime organic EL device using a distyryl compound as an organic light emitting material and styrylamine or the like added to the compound has been proposed (Patent Document 3). However, an additional improvement of the device has been requested because the device does not have a sufficient lifetime.
In addition, a technology involving the use of a monoanthracene or bisanthracene compound and a distyryl compound in an organic light emitting medium layer has been disclosed (Patent Document 4). In such technology, however, an emission spectrum shifts to longer wavelengths owing to the conjugate structure of the styryl compound, and hence a color purity deteriorates.
In addition, Patent Document 5 discloses an invention in which an aromatic amine derivative having an arylene group at its center and a dibenzofuran ring bonded to a nitrogen atom is used as a hole transporting material, and Patent Document 6 discloses an invention in which an aromatic amine derivative having a dibenzofuran ring, dibenzothiophene ring, benzofuran ring, benzothiophene ring, or the like bonded to a nitrogen atom through an arylene group is used as a hole transporting material. However, there are no cases where the derivatives are used as light emitting materials.
Patent Document 1: JP 11-3782 A
Patent Document 2: JP 08-12600 A
Patent Document 3: WO 94/006157 A1
Patent Document 4: JP 2001-284050 A
Patent Document 5: JP 3508984 B2
Patent Document 6: WO 07/125714 A1